Haunching needed or not?

[TheSeal]

Hi again,

Following on from my post last week about removing a concrete stump (now thankfully gone), project driveway can continue.

I've a few further questions I'm hoping somebody may be able to help with.
It's going to be a gravel drive on the appropriate membranes, hardcore, gravel grids, etc.

I'd like edging all the way around (as shown in the links below, green lines), rather than just across the front. The step will also be getting removed and replaced with a rectangular one. You can also see from the neighbours wall just how much above pavement height the old paved area was...

• https://photos.app.goo.gl/ChWaT8bLzD2a3Xsz5

• https://photos.app.goo.gl/4RZKKYnV9CtMQuJJ6

I'm aware that the white highlighted part labelled '1' in both pictures will need haunching behind as there will be no support otherwise. This area will be filled and paved and used to store the bins (because of the wall foundations, I can't get it to a level to allow me to go right up against the wall at the excavated height and the gas pipe is also under there).

However, all of other edges in green on the photos will be restrained by an existing structure such as house, step, partition wall, or pavement.

My first question; will those other edges in green need haunching or will the support provided from the existing structures behind them AND the support from the hardcore, grids and gravel in front of them be sufficient to secure them?

If haunching is required, everything online and on PavingExpert suggests to haunch behind, but I don't see how this is possible when flush against an existing obstacle?

My second (and hopefully final) question; when it comes to bedding, especially for the edgings for access from pavement to drive, will ST1 / C7.5 concrete be sufficient to take the car rolling over them, or would people recommend ST4 / C20? Or any other suggestions for that matter. I anticipate for 155mm bedding concrete with 60mm paver on top to bring to pavement height.

A few side notes:

• I intend on doing the edgings before laying down a membrane, or would people recommend membrane before edgings?

• I've excavated the length of one housebrick down; 215mm. I'm hoping that gives me the depth for membrane, 150mm compacted MOT, 10-15mm sharp sand (if needed), 28mm for gravel grid, plus enough gravel (20mm sized) to cover the grid by 10-15mm. The hope is to have the gravel stop about 5-10mm lower than the edging to help minimize migration.

Many thanks (and sorry for the length)
Dave

[Hotdog]

**Disclaimer: I'm no expert!**

My two penn'orth:

Block edgings bedded on correct depth of concrete should be fine as they are retained by the existing walls/path judging by the pics.
EDIT: Having said that, if you do go the gravel route; you may want to haunch the inside edge of the blocks to keep them in situ.

Personally I wouldn't skimp on the strength of the concrete when there are cars rolling on it. Cost differential between ST1 and ST4 would be negligible.

I don't think it matters regards membrane before or after edgings - pretty sure most put the membrane down after though...

With regards to the depth - you need to be 150mm below damp course once complete with paving/block - I don't know if this changes when using gravel, as it is highly permeable - but I'd stick to the 150mm rule personally.

Just a thought: If I were going to all that trouble excavating and laying edgings, I would 100% block pave the whole thing. You've already done the lion's share of the job! Sweeping that gravel back onto the drive every week from the pavement will be a right pain in the arse!

[TheSeal]

Hi Hotdog,

Thanks for the response.

Block edgings bedded on correct depth of concrete should be fine as they are retained by the existing walls/path judging by the pics.
EDIT: Having said that, if you do go the gravel route; you may want to haunch the inside edge of the blocks to keep them in situ.

I was thinking of a bit of haunching on the inside edge to do exactly that.

Personally I wouldn't skimp on the strength of the concrete when there are cars rolling on it. Cost differential between ST1 and ST4 would be negligible.

I agree, I was just curious as to whether there was any other reason why ST1 was used other than cost. I understand the benefit of ST1 for edges where a car will never roll over, but was a little unsure for where traffic passes over. As you said, the cost difference is negligible in the grad scheme of things

With regards to the depth - you need to be 150mm below damp course once complete with paving/block - I don't know if this changes when using gravel, as it is highly permeable - but I'd stick to the 150mm rule personally.

I'm still aiming for 150mm below DPM for finished height, it may be closer to 175-180mm as this will reduce the angle of slope from the house to pavement level.

Just a thought: If I were going to all that trouble excavating and laying edgings, I would 100% block pave the whole thing. You've already done the lion's share of the job! Sweeping that gravel back onto the drive every week from the pavement will be a right pain in the arse!

The reviews I've seen from using gravel grids and the edging slightly higher rather than flush suggest that migration isn't too much of an issue. Also, for me to consider block paving now, I'd need to excavate another 30-40mm to accommodate the additional sharp sand depth for the bedding layer. Unfortunately not feasible as I've got materials being delivered over the coming days. Hindsight is a wonderful thing

Another question after some further reading last night: I've seen some suggestions that a thin layer of gravel to be applied between soil and concrete to aid drainage and reduce soil erosion under the concrete, admittedly for larger concrete areas such as shed bases. Will this be needed in the base of edgings, or is it OK to place the bedding concrete directly on the compacted sub-grade?

Cheers,
Dave

[digerjones]

I'd block pave it also. If you've got 225mm out. Then 50mm pavior 30 sand 115 mm mot would be plenty. Everything else has been answered already